Importance, Source and Control of Bacteria Wilt Disease in Greenhouse Tomato (Solanum Lycopersicum L.) in Southern Ghana.

Abstract

Bacterial wilt of tomato is a devastating disease in greenhouse in southern Ghana where most greenhouses are sited. This study was conducted to assess farmer’s knowledge and experiences on the prevalence, detection, spread and control of the disease in greenhouses in Volta, Eastern, Central and Greater Accra regions of Ghana. The disease incidence and severity was also determined and the causal organism of the disease isolated from diseased tissues and characterized using morphological, biochemical, and molecular techniques. Sources of the bacteria inoculum in greenhouses were identified and some tomato cultivars were screened for resistance to the bacterial wilt disease. Questionnaires were administered to (50) greenhouse farmers purposefully selected using a database of greenhouse producers in southern Ghana provided by West Africa Agricultural Productivity Programme (WAAPP) between August and December 2017. The questionnaire investigated the background of greenhouse farmers and their knowledge and experiences on the prevalence, detection, spread and control of the disease in greenhouses. Frequency data was analyzed using descriptive statistical analysis (means and percentages) by means of EPI INFO version 7.2 software. Disease incidence was determined and severity scored using a 0-4 rating scale. Gram strain reaction test, potassium hydroxide solubility test, tobacco hypersensitivity test, bacteria colony morphology and reaction on 2, 3, 5-triphenyl tetrazolium chloride (TZC) were used to identify the causal organism. Multiplex polymerase chain reaction was used to determine phylotypes of the bacterial isolates. Plant samples, growth substrate, seeds and irrigation water collected from surveyed greenhouses were screened for the presence of the causal organism using polymerase chain reaction. Five tomato accessions (WACC1, WACC2, WACC3, WACC4 and WACC5) and a high yielding variety preferred by greenhouse farmers (EVA F1) were screened for resistance against the bacterial wilt disease in a screen house at Nungua Livestock breeding station. Seedlings were transplanted in a naturally infested coco peat and inoculated with 5 ml of a 108 CFU/ml bacterial suspension using the stem puncture technique. Disease severity was observed after inoculation and the area under disease-progressive curve (AUDPC) calculated for each variety. Results from survey indicated that 28% of greenhouse farmers knew the test for detection of the disease with 64% of greenhouse farmers having no knowledge of how the disease spreads. Majority (62%) used roughing and burying of the infected plant to control the disease. Out of the 54 greenhouses (domes) surveyed, only 12 had the infestation from the disease. Disease incidence and severity within greenhouses ranged from (5.9%-18.5%) and (0.5 – 1.2) respectively, with Greater Accra (18.5%) and the Eastern region (8.2%) with highest disease incidence. Central and Volta regions had no infestation of the disease in their greenhouses. Ralstonia solanacearum was identified as the causal organism of the disease and Phylotype I (Asian origin), Phylotype III (African origin) and Phylotype IV (Tropical origin) strains were identified from the study. The source of bacteria inoculum in the greenhouses were irrigation water and the growth media (substrate) used. All varieties tested were susceptible to the bacterial wilt disease, however, WACC 5 showed the least susceptibility to the bacterial wilt disease. Greenhouse farmers had little knowledge on the spread, detection and control of the bacterial wilt disease of tomato. The disease was detected in Greater Accra and Eastern regions disease incidence of 18.5% and 8.2% respectively. The causal organism was confirmed as Ralstonia solanacearum and the other sources of inoculum was irrigation water and the growth medium. Research on the use of resistant rootstocks in grafting and the screening of more varieties for resistance to the disease is recommended.